The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In wireless communication technology, transceiver circuits are used in various applications such, for example, cellular telephones, cordless telephones, pagers, global positioning systems, and other applications. A conventional transceiver chip typically includes a transmitter and receiver for performing the wireless communication function. One example of such a transmitter is the conventional Direct-Conversion Radio-Frequency (RF) transmitter which is used for multi-mode transmission with different modulation schemes.
Various components in a conventional Direct-Conversion Radio-Frequency (RF) transmitter introduce a linearity issue that can add noise (or otherwise degrade) the transmitter output signal. For example, a voltage to current conversion stage (commonly identified as a Gm stage) in a conventional Direct-Conversion RF transmitter typically introduces non-linear components to the transmitter output signal when the Gm stage performs a voltage to current conversion of signals prior to the transmission of the transmitter output signal. The non-linear components can introduce undesired frequency tones which degrade the wireless transmission process because these undesired frequency tones can lead to, for example, noise or other interference that affects the transmitted signal in the receiver side.
Additionally, in versions of a conventional Direct-Conversion RF transmitter that does not use the Gm stage, the analog mixer in the conventional transmitter also presents a linearity issue because the voltage signal that is subject to the switching function of the analog mixer typically also introduces non-linear components to the transmitter output signal. The analog local oscillator (LO) can also introduce non-linear components to the transmitter output signal.
Additionally, the analog base-band filter and analog base-band Gm can introduce noise in a receiver frequency band (RX-band noise). This_Rx band noise may negatively affect the receiver in remote devices and/or may negatively affect the receiver in the same device if the device is based on the FDD (frequency-division duplex) standard that requires the transmitter and receiver are on at all times.